Not very many years ago, what is now often referred to as the Tanglossian Paradigm" reigned supreme in evolutionary biology. It was widely assumed, at least implicitly, that a central function of biology was to analyze organisms in such a way that the adaptive advantages, indeed the optimality, of their various features could be discerned. If it occurred to some imaginative biologist that snails would have been much better off running on caterpillar tracks, then some work would be needed to show why they were really better off dragging themselves around on a sheet of slime. For if they would have been fitter with the caterpillar tracks, then the omnipotent force of natural selection would surely have seen to it that they were so equipped. I exaggerate, but not all that much.